Plasma deposition and etching processes for fabricating semiconductor integrated circuits have been in wide use for decades. These processes typically involve the formation of a plasma from plasma-generating gases that are exposed to electric fields of sufficient power inside the processing chamber to cause the gases to ionize. The temperatures needed to form these gases into plasmas can be much lower than needed to thermally ionize the same gases. Thus, plasma generation processes can be used to generate reactive radical and ion species from the starting gases at significantly lower chamber processing temperatures than is possible by simply heating the gases. This allows the plasma to deposit and/or etch materials from substrate surfaces without raising the substrate temperature above a threshold that will melt, decompose, or otherwise damage materials on the substrate.
Exemplary plasma deposition processes include plasma-enhanced chemical vapor deposition (PECVD) of dielectric materials such as silicon oxide on exposed surfaces of a substrate wafer. Conventional PECVD involves the mixing together of gases and/or deposition precursors in the processing chamber and striking a plasma from the gases to generate reactive species that react and deposit material on the substrate. The plasma is typically positioned close to the exposed surface of the substrate to facilitate the efficient deposition of the reaction products.
Similarly, plasma etching processes include exposing selected parts of the substrate to plasma activated etching species that chemically react and/or physically sputter materials from the substrate. The removal rates, selectivity, and direction for the plasma etched materials can be controlled with adjustments to the etchant gases, plasma excitation energy, and electrical bias between the substrate and charged plasma species, among other parameters. Some plasma techniques, such as high-density plasma chemical vapor deposition (HDP-CVD), rely on simultaneous plasma etching and deposition to create features on the substrate.
While plasma environments are generally less destructive to substrates than high-temperature deposition environments, they still create fabrication challenges. Etching precision can be a problem with energetic plasmas that over-etch shallow trenches and gaps. Energetic species in the plasmas, especially ionized species, can create unwanted reactions in a deposited material that adversely affect the material's performance. Thus, there is a need for systems and methods to provide more precise control over the plasma components that make contact with a substrate wafer during fabrication.